Pascal (Lazarus/Delphi)

Regular Expression with Named Capture Groups

See more Regular Expressions Examples

Demonstrates regular expressions with named capture groups.

See the sample code below.

Note: Chilkat uses PCRE2. See PCRE2 Regular Expressions
Also see: PCRE2 Performance

In PCRE2, named capture groups allow you to assign a name to a capturing group, making it easier to reference by name instead of number.

Syntax

(?<name>pattern)

or

(?'name'pattern)

Example

(?<first>\w+)\s+(?<last>\w+)

Applied to:

"John Smith"

Produces:

• first: John
• last: Smith

Pascal (Lazarus/Delphi)

program ChilkatDemo;

// Demonstrates using the Chilkat Pascal wrapper via the C bridge DLL.
// Builds as a console application under Lazarus (FPC) or Delphi.

{$IFDEF FPC}
  {$MODE DELPHI}
{$ENDIF}
{$APPTYPE CONSOLE}

uses
  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}
  SysUtils,
  CkDllLoader,
  Chilkat.JsonObject,
  Chilkat.StringBuilder;

// ---------------------------------------------------------------------------

procedure RunDemo;
var
  success: Boolean;
  subject: string;
  pattern: string;
  sb: TStringBuilder;
  json: TJsonObject;
  timeoutMs: Integer;
  numMatches: Integer;

begin
  success := False;

  subject := 'John Smith';
  pattern := '(?<first>\\w+)\\s+(?<last>\\w+)';

  sb := TStringBuilder.Create;
  sb.Append(subject);

  json := TJsonObject.Create;
  json.EmitCompact := False;

  timeoutMs := 2000;
  numMatches := sb.RegexMatch(pattern,json,timeoutMs);
  if (numMatches < 0) then
    begin
      //  Probably an error in the regular expression.
      //  Suggestion: Use AI to help create and/or diagnose regular expressions.
      WriteLn(sb.LastErrorText);
      Exit;
    end;

  //  Examine the matches:
  WriteLn(json.Emit());

  //  Here is the JSON showing the matches.
  //  Important:  Capture group 0 always contains the entire match — that is, the portion of the input string that matches the full regular expression.

  //  {
  //    "named": {
  //      "first": 1,
  //      "last": 2
  //    },
  //    "match": [
  //      {
  //        "group": [
  //          {
  //            "cap": "John Smith",
  //            "idx": 0,
  //            "len": 10
  //          },
  //          {
  //            "cap": "John",
  //            "idx": 0,
  //            "len": 4
  //          },
  //          {
  //            "cap": "Smith",
  //            "idx": 5,
  //            "len": 5
  //          }
  //        ]
  //      }
  //    ]
  //  }

  //  The capture group index is obtained by looking up the name in the JSON result.
  //  For example:

  json.I := json.IntOf('named.first');
  WriteLn('first: ' + json.StringOf('match[0].group[i].cap'));

  json.I := json.IntOf('named.last');
  WriteLn('last: ' + json.StringOf('match[0].group[i].cap'));

  //  Output is: 

  //  first: John
  //  last: Smith


  sb.Free;
  json.Free;

end;

// ---------------------------------------------------------------------------

begin

  try
    RunDemo;
  except
    on E: Exception do
      WriteLn('Unhandled exception: ', E.ClassName, ': ', E.Message);
  end;

  WriteLn;
  {$IFDEF MSWINDOWS}
  WriteLn('Press Enter to exit...');
  ReadLn;
  {$ENDIF}
end.